/Engine/Source/Editor/LevelEditor/Public/ILevelEditor.h
Get an array containing weak pointers to all 4 Scene Outliners which could be potentially active
[TArray](API\Runtime\Core\Containers\TArray)< [TWeakPtr](API\Runtime\Core\Templates\TWeakPtr)< [ISceneOutliner](API\Editor\SceneOutliner\ISceneOutliner) > > GetAllSceneOutliners() const